(+1/2) + (+1/4) =2/4+1/4=3/4
(+1/5) + (-3/5) =-2/5
(-2/7) + (+9/7) =7/7=1
(-3/2) + (-5/6) = [(-3×3)-5)/6=-14/6==-7/3
(+3/4) - (-3/8) =[(+3×2)+3]/8=9/8
(+1/2) - (-1/6) = (1×3+1)/6=4/6=3/3
(-1/3) - (-2/3) ==(-1+2)/3=1/3
13/24 x 48/39 =
(39×13-48×24)/24×39=645/936
